The term lidar is an acronym for light detection and ranging. Lidar systems employ intense pulses of light, typically generated by lasers, and large telescopes and sensitive optical detectors to receive the reflected pulses. They are most commonly used to measure the composition and structure of the atmosphere, such as by tracking weather balloons, smoke puffs, reflections and scattering effects of clouds, and rocket trails. The very narrow beam width, narrow line width, and ultra short pulses of the laser make it possible to optically probe the atmosphere with exceptional sensitivity and resolution.
A contrail or condensation trail is the visible trail of condensed water vapor or ice particles left behind an aircraft, an airfoil, etc. in motion through the air. There are three kinds of condensation trails or vapor trails: the aerodynamic type, caused by reduced pressure of the air in certain areas as it flows past the aircraft; the convection type, caused by the rising of air warmed by an engine; and the engine-exhaust, or exhaust moisture, type, formed by the ejection of water vapor from an engine into a cold atmosphere.
Lidar systems have been used to measure the particles that comprise contrails. The foregoing is accomplished by measuring the optical backscatter of the particles in a portion of the contrail.
Systems have been installed in aircraft to measure the optical characteristics of the atmosphere in a region near the airplane. However, optical techniques have not been utilized to measure the exhaust plume or contrail region near an airplane in flight.
Prior art device did not permit a pilot to monitor the size of the particles inside his exhaust plume at a distance of several hundred meters behind his airplane. Thus, one of the disadvantages of the prior art was that the pilot was unable to monitor the size of soot particles, etc. in the exhaust plume or contrails to minimize pollution emissions of the jet engines of the aircraft.
Another disadvantage of the prior art was that the pilot was unable to monitor the size of particles in the exhaust plume or contrail to more efficiently use the engines of the aircraft.
Reference may be had to the following patents for further information concerning the state of the prior art.
In U.S. Pat. No. 4,251,733, issued Feb. 17, 1981, entitled "Technique for Simultaneous Particle Size and Velocity Measurement" to Hirleman, Jr. there is disclosed the analysis of backscattered light from a laser source for purposes of simultaneously determining particle size and velocity.
In U.S. Pat. No. 4,492,467, issued Jan. 8, 1985 entitled "Measurement of The Size of Particles" to Drain et al. there is disclosed a method of determining the size of spherical particles by detecting backscattered light from a laser source.
In U.S. Pat. No. 4,497,577, issued Feb. 5, 1985 "Steam Wetness Measuring Apparatus" to Sato et al. there is disclosed a steam wetness measuring apparatus wherein information derived from backscattered light is processed to determine the particle size distribution of the water droplets.
In U.S. Pat. No. 4,871,251, issued Oct. 3, 1989 entitled "Apparatus And Method For Particle Analysis" to Preikschat et al. there is disclosed an apparatus and method for analyzing the size and number of particles in a fluent medium using backscattered light from a laser light source.
In U.S. Pat. No. 5,047,653, issued Sep. 10, 1991 entitled "Device On Board A Moving Vehicle To Obtain Signals Representative Of The Relative Speed of The Vehicle With Respect To An Ambient Fluid" to Garcia et al. there is disclosed an apparatus which is mounted on an aircraft that determines the relative speed of the aircraft with respect to an ambient fluid by measuring the light reflected by particles moving through a measuring volume of the ambient fluid.
In U.S. Pat. No. 5,094,532, issued Mar. 10, 1992 entitled "Method And Apparatus For Measuring Small Particle Size Distribution" to Trainer et al. there is disclosed a method of measuring size and distribution of moving particles within a scattering medium by comparing the frequency of the scattered light to the nonscattered light.
In U.S. Pat. No. 5,116,124 issued May 26, 1992 entitled "Measurement System For Scattering of Light" to Huttmann there is disclosed an apparatus using backscattering laser light for the measurement of atmospheric visibility or optical density. The apparatus may be mobile by being used in vehicles.
In U.S. Pat. No. 5,206,698 issued Apr. 27, 1993, entitled "Lidar Arrangement For Measuring Atmospheric Turbidities" to Werner et al. there is disclosed a lidar arrangement for measuring atmospheric turbidities wherein a signal processing unit distinguishes between different kinds of visibility obstacles such as fog, rain, snow or solid obstacles. The arrangement may be made mobile.